This invention relates to a vaporizer for vaporizing liquefied gases such as liquefied petroleum gas, and in particular, to heat exchangers used in liquefied gas vaporizers.
Vaporizers for the controlled vaporization of liquefied gases are generally known. One electrically heated liquefied petroleum gas (LPG) vaporizer is disclosed in U.S. Pat. No. 4,255,646. Another liquefied gas vapor unit is disclosed in U.S. Pat. No. 4,645,904. Typically, the vaporizer includes a hollow, pressure vessel having a liquefied gas inlet near a lower end and a gas vapor outlet near a closed upper end remote from the liquefied gas inlet. A heating core is typically disposed within the pressure vessel, usually positioned close to the lower end. A plurality of resistive electric heating element may be embedded within the heating core.
Such vaporizers using electric heating elements often require the use of a temperature sensor coupled with a time proportional controller for applying power to the heating elements with a periodic on/off duty cycle determined by the deviation of the core temperature from a predetermined set point. An increase of the core temperature above the set point proportionately reduces the on time of the duty cycle, while a decrease of the core temperature below the set point proportionately increases the on time of the duty cycle. Control circuitry including switches are required.
The vaporizer may also have liquefied gas sensing means communicating with the interior of the pressure vessel near its upper end, below the gas vapor outlet. The liquefied gas sensing means is typically an overflow sensor or xe2x80x9cfloat switchxe2x80x9d for sensing the level of liquefied gas in the pressure vessel and controlling a valve that opens and closes to stop the flow of liquefied gas into the pressure vessel. Accordingly, the valve is controlled to open the pressurized flow of liquefied gas into the pressure vessel and to shut off the flow before the liquefied gas fills the gas vapor head space and liquefied gas floods through the outlet of the vaporizer.
A problem with such known vaporizers is the need to control the on/off duty cycle of the electric heater elements to prevent overheating. The circuitry required creates safety concerns, and in addition, maintenance and reliability concerns are created. Further, the circuitry increases the cost of manufacturing the vaporizer.
The present invention resides in a vaporizer for vaporizing a fluid with a heat exchanger having a mass of thermally conductive material and a tube embedded therein to transfer heat from the thermally conductive material to the contents of the tube, and a plurality of positive temperature coefficient heater elements thermally coupled to heat to the thermally conductive material. The tube has an inlet portion to receive the fluid to be vaporized and an outlet portion to discharge the vaporized fluid.
In one embodiment of the vaporizer, the heat exchanger has a block of thermally conductive material with a tube embedded therein and with a planar surface portion. The heater elements are each flat with a substantially planar surface arranged in coplanar parallel arrangement with the planar surface portion of the block. The block further includes an end surface, and the inlet and outlet portions of the tube project from the end surface of the block.
In this embodiment, the heater elements are electrically coupled in parallel and each has a cure temperature greater than the saturation temperature of the fluid to be vaporized. The heater elements are connectable directly to an electrical power source without regulation by the vaporizer of the power supplied by the power source. The tube extends within the block along a curved path.
In one embodiment, the vaporizer includes a first heat exchanger having a first block of thermally conductive material with a first tube embedded therein to transfer heat from the thermally conductive material of the first block to the contents of the first tube, with the first block having a surface portion. The first tube has an inlet portion to receive the fluid to be vaporized and an outlet portion to discharge the vaporized fluid. The vaporizer further includes a second heat exchanger having a second block of thermally conductive material with a second tube embedded therein to transfer heat from the thermally conductive material of the second block to the contents of the second tube, with the second block having a surface portion. The second tube has an inlet portion to receive the fluid to be vaporized and an outlet portion to discharge the vaporized fluid. The first and second blocks are arranged with the surface portions thereof facing each other, and the outlet portion of the first tube connected to the inlet portion of the second tube. This embodiment further includes a plurality of positive temperature coefficient heater elements. Each heater element is formed with first and second opposed surfaces. The heater elements are positioned between the first and second blocks with the first surfaces of the heater elements in thermal contact with the surface portion of the first block and with the second surfaces of the heater elements in thermal contact with the surface portion of the second block.
The inlet and outlet portions of the first and second tubes project from the respective first and second blocks. The vaporizer further includes at least one member holding the first and second blocks tightly together with the heater elements positioned therebetween clamped tightly between the surface portions of the first and second blocks.
In this embodiment, the heater elements may be arranged in a single row alignment. The heater elements are elongated and each is oriented with a longitudinal axis arranged transverse to a direction of the row, and every other one of the heater elements in the row is longitudinally offset from the adjacent heater elements.
The first block further includes an end surface, and the inlet and outlet portions of the first tube project from the end surface of the first block. The second block further includes an end surface, and the inlet and outlet portions of the second tube project from the end surface of the second block. The end surfaces of the first and second blocks are arranged one adjacent to the other, and the outlet portion of the first tube is connected to the inlet portion of the second tube at a location adjacent to the adjacent end surfaces.
In some embodiments, the vaporizer includes a chamber with the thermally conductive material being a fluid contained within the chamber. The heater elements are immersed in the thermally conductive fluid.
In some embodiments the tube includes a coiled portion embedded in the thermally conductive material. The thermally conductive material may have a cylindrical shape with a longitudinal axis and the coiled portion of the tube may be arranged about the longitudinal axis. The heater elements may each include a rod shaped portion embedded in the thermally conductive material.
A method is also disclosed for forming a low-profile vaporizer with the foregoing constructions.
Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.